 So we have been discussing about the soil constituents and I had talked about solid phase, liquid phase and gaseous phases and we were discussing the organic matter in soil. So one of the biggest issues with organic matter is that if organic matter is present in substantial matter. So as the OM increases, I use normally this sign alright. So as this content increases, this becomes more and more problematic for geotechnical engineers. So later on you will realize that the more the organic content in the soil, you cannot even modify this. So those of you who might get a chance to work on ground modification or soil stabilization, these are big subjects. So I am not going to go in the details of these but those of you who are very curious to learn about it, please do Google search and you will get lot of information regarding soil stabilization and ground modification. These are the techniques which are nowadays used for making infrastructure in the challenging and problematic soils as I discussed the other day. So peat is the most notorious thing, peat you must, we had discussed about the muskeg also other day. So these are the soils which have posed a serious problem to the professionals. So higher the organic matter, the problems become difficult to stabilize. The big issue is that as the organic matter increases, the soil will not react with cement. So most of the marine clays which have a substantial amount of marine clay as organic matter is very difficult to stabilize them but I am sure you must be seeing in contemporary world most of the stabilization or most of the construction is going on in the coastal regions. Government of India, Sagar Mala project is a very good example. So all along 11,000 kilometers of the coastal line, they are trying to create infrastructure. This is just like you know in Hindi you call it dal dal or in English you call it muck and the other day somebody was sitting here and he was you, someone else I do not know. So you are talking about you know muck, remember maybe first or second lecture. So this is the type of the soil which is very difficult to negotiate with. So most of the construction which is going on the coastal region requires a stabilization. One of the ways of stabilization would be grouting. Why I am teaching you all these things, these are the subjects which have to be practiced by people like you. Many of you say there are no jobs. I can assure that there are so many jobs, there are so many specialized things to be done which cannot be done by the right guys. So these are the areas in which you can think of exploring the possibilities. Another issue is that this material has a very poor shear strength and very high compressibility. The next constituent of the soil would be yes water and this was what number was the water in the list of constituents 4, 5, this would be 5 alright. Very soon when we will realize you know how water influences the overall characteristics of the soil, when we will discuss these things in details you will come to know that water is the component or the constituent of the soil which controls its all engineering properties. And when we talk about the engineering properties, these are mostly shear strength. This is what I will be discussing in the second course. Shear strength is a dedicated chapter, maybe I will spend about 16 to 18 lectures on you know defining and how to determine the shear strength is a big subject in soil mechanics. The compressibility and hydraulic conductivity and when you come in the domain of the research you will realize all sorts of conductivities would depend upon the moisture content including how heat migrates in the system, how current migrates in the system, how electromagnetic flux will migrate in the system. Well this is the beyond the scope of undergraduate soil mechanics or geotechnical engineering I will not be discussing this. This is a recent discussion in geomechanics, we call this as a you know flux migration and the flux could be of thermal, electrical, electromagnetic, it could be bacterial, it could be whatever you might think of a combination of the two and this forms the coupled phenomena in western world a lot of people are working in these areas, they have a lot of funds and they want people like you to join their research groups. So situation is not so bad as you think. Here shear strength is basically the strength of the soil mass once it gets sheared. So suppose if I take a piece of paper alright and normally the word which you use is tear alright, so what I am doing look at the motion of my hands, the motion of the hands is in opposite direction clear, one and this is on the other side it is a tearing process but tearing itself is initiated because of the shearing at a plane and as I said this is something which is to be discussed separately. When earthquake comes this is the strength which is required in the material otherwise then everything will become like liquid you remember we were talking about the liquefaction of the soil that the soil behaves like liquid okay. So here we use another term because of the presence of water we call this as PWP poor water pressure which is very equivalent to the blood pressure of the human body. So what happens suppose your blood pressure shoots up you see somebody and you know you feel very angry, annoyed hyper active. So what happens you start sweating your blood vessels immediately throw a lot of blood on your face, face becomes red and if blood pressure shoots too much what is going to happen you collapse same thing is going to happen in soils also if by any chance the poor water pressure becomes extremely high the system becomes a critical patient to be treated by a surgeon alright and what are the surgeries these are surgeries either I will modify the situation or I will enhance the properties. Other way low blood pressure what happens most of the people collapse because of the low blood pressure also. So this port of pressure is a very tricky thing in geomechanics most of the time the pressure will develop in the soils in the pores we will be talking about what are the pores clear. So most of the time the water pressure develops in the pores because of the external loading a good example would be there is a railway track and there is a train of let us say 45 bogies politicians would be say that we will make it 55 bogies 65 bogies 100 bogies is it not and geotechnical engineer says no it is not possible to have more than 45 bogies why there is an answer to this because the railway tracks have been designed in such a manner that when the rails move the type of pore temperature which is going to develop will sustain the external loading appropriately clear. From here comes the or from this is a starting point of the of the professionals like you who might get converted into earthquake specialist soil dynamics you will be dealing not with the static situations you will be dealing mostly with the impact vibrations movement of vehicles movement of traffic missile coming and hitting a shielded object is all dynamic cases clear. So I will be very interested in seeing that these type of situations how they are going to enhance or decrease the pore order pressure of the material the logic is or the funda is if I am dealing with the coarse grain materials like sands gravels clear even if the pore order pressure develops it will dissipate fast there are guys who are very sensitive you say something they will immediately cry after that everything becomes normal 2-3 minutes they forget everything. So these soils which are coarse grain are blessed they dissipate pore order pressure which gets developed because of the external loading quickly hence damage is done less on the other side there are guys who keep everything in their heart and mind you say something today and the reaction will come after 5 days there are personalities correct. So most of the fine-grained materials would have a severe problem of pore order pressure developing because of the external loading. So suppose I am doing a railway track in the coastal belt from Bombay to let us say Kochin alright where you are passing through the marine clays you have to be very careful about this pore order pressure you have to dissipate it clear if this remains inside the system and it becomes very high there will be a loss of strength as I said people may collapse okay. Normally we will be talking about these things in details when we discuss consolidation mechanism there is a phenomenon where if I apply the load the pore order pressure develops immediately in the soils and then depending upon the material property the type of a person you have to wait how long this guy takes to release all the emotions clear to release all the pore pressure and then we will model it accordingly. So this is a something which is we will be discussing for at least 3-4 lectures minimum. So logic says if you apply the external loads alright the pore order pressures will build up. So the moment external loads are applied the pore order pressure goes up okay. Now as a surgeon as a doctor as a professional as a knowledgeable person I have to tackle the situation how best I can tackle the situation. One important thing about the water is that water cannot take shear is it not is this correct water can be only compressed it cannot be sheared because it is a property of the material. So imagine the soils which have enough moisture in them we are discussing about the water water is also sometimes known as moisture content alright. So the more the water more the moisture content the chances of pore order pressure getting developed in fine grain soils are higher as compared to the coarse grain soils the moment you externally loaded pore order pressure becomes very high strength is getting lost the question is what water is doing water takes only compression or the compressive loads it cannot take any shear stresses. In fact more the moisture content more the water content the shear strength is going to be absolutely less and that is the reason if you go and enter into a marshy deposit chances are that you will sink you cannot walk clear. I gave you this analogy last lecture also you are on a beach and you know it is a dry sand and if I ask you to run you cannot run but suppose the sands become wet and you can dry the car also on that next time when you go to joe beach please try this then only you learn soil mechanics. So what water does water reinforces the material also it acts as a reinforcement what you are using in the concrete in the form of the rebars and the steel. So the more and more water which is present because of the capillary action gives more shear strength so water is the main thing and we have to study quite in details how it has to be modeled. Water is the carrier of the dissolved salts minerals alright. Now I think you can realize this if I want to stabilize if I want to modify the soils what I will be doing I will take some cement slurry water is the carrier and I am injecting dissolved salts into the system to make it strong very similar to the one which doctors do by injecting a you know ampule or something injection in your body if you are having some deficiency or if you are having some disease and so on there are a lot of similarity between all these things. Now it so happens when we talk about the dissolved salts there are few passive salts there are few active salts so carbonates, bicarbonates, sulphates, chlorides these are the ones which are naturally occurring in the water and this gets impregnated I hope you understand the word impregnation impregnation means they become a part of the system. So they get impregnated into the soil and hence soils would have salts coming from different agencies. So for that matter if you take a sample from Poway Lake or let us say from Bay of Bengal or anywhere from water body if I squeeze out the soil and whatever solution comes out is just like the reflection of what type of problems the soils would be having and how to treat them. This is what is known as pore solution sampling the way the blood sampling is done from your body. Doctors and pathologists take few drops of blood and they give you all parameters correct. So similarly I can take out some part of the pore water I can analyze I can diagnose the problem so this is a big science and big work which is going on everywhere in the world. This water is also responsible for soil water interaction alright that means look at the dams where you are storing water. So there is no fun in creating a body of the dam through which the water percolates all the time I cannot store water then is it not. So the whole idea is that I should be storing water in a embankment or a dam body which is impervious. So when soils come in contact with water there is interesting interaction which goes on. Some of you who will be go for higher studies or in profession you will realize soil water interaction this could be soil structure interaction this could be soil fire interaction this could be soil microbial interaction this could be soil what else it could be soil contaminant interaction very nice. So keep on replacing or adding terms to this and this becomes an interaction problem and interaction problems are mostly solved by the concepts of mechanics this is part okay. Then comes the air air and water these are opposite to each other. So if water gives shear strength to the system strength to the system the more and more air if it is present in the soil mass the system becomes first of all unsaturated. So suppose if I say that soil mass has lot of air in it and very less moisture. So this becomes the state of unsaturated soil and this state of the soil I am not going to discuss in third year soil mechanics or geotechnical engineering. Those of you are interested please visit my lab see what are the special equipment which are required to model the unsaturated state of the soils is totally different world altogether and I am not going to cover this here. So this is the unsaturated soil mechanics or mechanics of unsaturated soil but please remember this is more realistic than the one which we are going to discuss in the entire course because what we are going to discuss is a simplification of the real life situation which is extremely complicated. Because the dynamics of the air inside the soils is going to be extremely complicated and you require different tools to study this or measure this. Sometimes this is also known as VEDOS zone many of you who go for you know summer trainings and internship and particularly those of you who go to France I mean I get the feedback that we are not teaching you guys properly I get most of the feedback from different parts of the world about our students. So remember this subject is also known as VEDOS zone modeling. So if you end up in ENPC or EPFL so it is the land. So there nobody understands mechanics of unsaturated soil this is what is known as the VEDOS zone. Sometimes they write it as VEDOS also both are correct do not fight with them alright. VEDOS V-A-D-O-S-E VEDOS or VEDOS sometimes we also call this as a partially saturated soils there are different names given to this partially saturated soils. Sometimes people also call this as variably saturated soils also alright. Those of you who may get a chance to work in nuclear industry particularly or the thermo active structures which are being talked about these days you know entire west is doing lot of research on energy geotechnics I think I talked about this earlier. So this is where you will be using all these terms. So what happens if a saturated soil mass if you start with it comes in contact with the heat flux what is going to happen the water present in the soil will get converted into air phase is this correct. So at elevated temperature or pressure also I hope you understand this. So I have created two situations if I elevate the temperature of the soil the water which is present in the soil pores will try to get converted into vapors and these vapors will migrate. Second thing is what I will do with the pressure I have to drop down the pressure I have to increase the pressure drop down the pressure you are right. So then what is going to happen all your points which you have studied in chemistry and physics sublimation point freezing point vaporization point all what else salt concentration point all those can be applied over here now. So look at this simply what I have done I have just used two terms and the realm of the subject realm is the regime you know the scope of the subject changes completely are you realizing it is a very interesting material. So the moment you heat it up or suppose if I say no I am going to freeze it minus delta T the connotation changes completely. So those of you who might go to Canada Germany all this western world where most of the time the soils remain frozen this becomes the frozen state of the soil mechanics correct or frozen state of the soils and what are the mechanics of that arctic regions polar regions lot of research is going on in this area in our own country in the northeast in the Himalayan reaches you know there are lot of research centers which are doing research on frozen state of the soils. So please remember we are not talking all these things in detail because these are the research ideas this is okay any question now when you are doing this water to air the saturation is decreasing water saturation is decreasing when you are heating it delta T let me create two situations out of it so delta T is positive and this is negative alright. So in this case when it is delta T is positive you are doing heating the saturation of the soil is going to change and when you are freezing it we talk about the saturation of ice content or ice content in the soil. So depending upon the regions in which you are you have to establish the material properties accordingly this is part clear this also opens up interesting concept check on net who are the guys working on THMC thermo hydro mechanical coupling sorry chemical coupling thermo hydro mechanical chemical biological coupling. So you have a lot of scope for practicing in geotechnical engineering alright the application comes here read this whenever you get time please read this and I am sure once you go into the implications part you will realize how much powerful these subjects are sir what does the shears what happens to the shear strength if air content increases oh very nice this pore of pressure which we are talking about is a component of two types of pressures one is the water and second one is the air alright. So as long as we deal with the conventional subject we say that there is no air by forcing the material to be saturated remove all the air but in real life it is not going to happen so this water will contribute UW pore of pressure and this will contribute to U air. So the correct modeling of the soils would be when you measure this also compute this also and take it into your account but for God sake please forget about unsaturated soils right now this is okay but now you are much ahead of your third year fourth year status like this thing people do not know even at the PG level believe me but once you know this now you device several equipments so that you can measure pore air pressure directly and these experiments are very very expensive our lab has all these facilities okay so another phase you know or the constituent of the soil would be minerals what are the minerals which are present in the soil the logic is same as I said last time you know if you have minerals in the soil just like the minerals in your body particularly for those of you who are very much eager to be good industrialist or good researchers interdisciplinary practitioners so for all of you you know this is going to be useful see the first thing is that minerals are to be identified and later on they have to be quantified the characteristics of the soil would largely depend upon the type of minerals it has and I hope you can realize that most of the minerals could be a genetic link between the soils and the rocks somebody asked this question long back so the way the weathering has occurred the way the transportation has occurred the way the mineralogy has changed over the years millions of years clear the system is going to behave or perform so first thing is identification second is quantification and third would be correlation this is more of a doctor's profession is it not you do the diagnosis first identify by symptoms or by doing diagnostic tests quantify the problem since how many days you are having this symptom and then remediation correlation understanding the issues and so on so it so happens that most of the elements of which the crust of the earth is constituted are listed over there so these are the elements of earth normally please get some time to go through the facilities which are evaluated Bombay very unique facilities these are known as XRD XRF SEM so you take the sample of the soil and put it in this type of equipment do the analysis and you will find that these are the elements which we are interested in we call them as percentage by weight oxygen silica and aluminum iron calcium sodium potassium magnesium and others alright and what you notice is that oxygen silica and alumina would constitute about 80 to 90 percent of the everything where these type of investigations become important in a profession like me where something has failed contractor has used the wrong material and I want to catch him this has become a legal case where I have to submit a report in the court that well all these things went wrong and hence he should be penalized the damages should be charged and so on all these type of negotiation arbitration which are happening in the court of law people like you and me have to help the court so this is what is known as elemental analysis all the minerals are containing these elements number one clear now we have to talk about the atomic structures you thought that after 10 plus 2 chemistry and physics this is not going to haunt you ever it is not like this the basics of the soils are you know again the atomic structure of the material so the clay minerals are made up of two distinct structural units the first one is known as tetrahedron and the second one is known as octahedron you must be aware of all this in chemistry courses you must have done clear tetrahedron and octahedron so there is nothing difficult to study silicon is here look at the atomic size 0.26 nanometers you have silicon at the center and then for oxygen atoms clear and then when you have aluminum octahedron you have alumina or magnesium and followed by either hydroxyl iron or it could be oxygen atom is this correct so these are the basic units rest of the things is the combination of this so we have octahedron we have tetrahedron and combination of these are going to form clay minerals so this is the tetrahedral sheet remember the spelling tetrahedron and tetrahedral so when several units of tetrahedron sit together they form a tetrahedral sheet so look at this this is sort of a bridging you know so what is going to happen in the holes which are getting created these are the parking lots other day I gave you an example about you know the skin care so you use clays and you put them on skin and then you peel them off so what happens all your sweat negative charges which are present in the skin bacteria it gets removed why where they are going parking places holes now these holes are also very responsible for accommodation of water molecules so suppose if I want to make a metrogel the basic structure of the mineral will remain same I will create more and more hexagonal spaces parking lots where the water molecules will go and sit because of hydrogen bonding I can replace this water by ions also potassium chloride hydrochloric acid calcium hydroxide and so on whatever it depends upon in what profession you are clear so these are the places where most of the ions will go and sit so the more and more ions which you can pack into this space makes clay a zeolite and then it has a medicinal value then it has a chemical value then it becomes a you know what do you call it as catalyst you add catalyst for different processes alright so it is all the parking place which you create by synthesis in the laboratory which is going to create this type of situation next for the sake of simplicity this is how we denote the sheets so a tetrahedral sheet is normally depicted like this alright rhombite and silica because remember there is a third dimension also associated to that which goes up to infinity so all these minerals will be having infinite length as compared to their thickness and the height and this is the alumina octahedral sheet yellow color clear now the question is suppose if you are making the tufts for cricket pitches and cricket control board will ask you give me a soil which should behave like this for five days or for let us say one full day T20 match water holding capacity is the most important thing that means these minerals should be holding the water despite all mechanical damages which the system is undergoing despite all the mechanical impacts which system is going to undergo clear when you throw a ball is of some weight momentum transfer water coming out of the plates of we call them as plates also very thin sheets so you have to design like this clear then somebody says on the pitches I will have grass also unlike somebody will say no this space should not have any grass so what type of minerals are going to present which are going to act as a nutrients for the vegetation is also a very important question I can feed all these things and I can do engineering with the minerals so this is a new subject in our you know realm our zone our our interest where you can create different type of minerals for their different requirements now see what happens if you have different clay minerals we can create either kaolin or heloisite this is the first group this is a clay mineral most of the powders which you use white color be it in washing powder we eat in soaps detergents anywhere toiletries cosmetics all kaolin all right what what powder does it absorbs sweat clear so these minerals would have some capacity that there is octahedral sheet and then on the top of this you have a tetrahedral sheet this becomes a kaolin or heloisite sometimes is also known and one is to one clay all right one silica one alumina combination of the two this becomes kaolin or heloisite sometimes we have two is to one so we have two tetrahedral sheet one octahedral sheet you know composited into this system those of you are very interested in this please read it is a typical structure of kaolin and I am sure you will be surprised to see what are the applications of the kaolin read this which I have written over here kaolin is used for making paper paint pottery cosmetic toiletries and in pharmaceutical industry these industries cannot survive unless an expert geotechnical engineer is there to help them and then later on comes the extrusion process which is nothing but your shear strength parameters go to a factory where the biscuits are made or you know chapati is the way the chapatis are done so what you are doing you are rolling them and then you are sometimes if I do it I will make sure that the chapati gets torn off clear but when experts hand do it gets rolled beautifully in a circular very thin sheet so there is a difference in experience and practice so this is another application of shear strength so I will make a dough of these minerals and I will extrude them to get wim bar soap bar lipsticks of different sizes whatever clear papers of different sizes and so on so this is the structure of the kaolin one nanometer is 10 to power minus 9 meters this is the formula for kaolin alumina silica sheets put together typically spacing is 72 0.7 to nanometer and this could be because of the oxygen shearing and typically 70 to 100 years layers are there and as I said they will extend into infinity and kaolin is a very stable material and that is the reason it is used for making portries so chances are that kaolin will not absorb moisture much because there is a hydrogen bond between the two combination of alumina and silica and hydrogen bond is a very strong one you cannot break it so easily so that is the reason for making portries kaolin or kaolinite is used alright and this is a stable system then comes halosite halosite is another mineral which is of kaolinitic family this is hydrated and it is of tubular structure most of these minerals are either platelets or tubular structures if you can remember this formula you can remember the only difference between kaolinite and halosite is that there are 4 water molecules which get added up to the kaolin alright so this becomes hydrated so calcium oxide put in water hydration occurs calcium hydroxide get formed alright is this okay then comes the monodonite people have a special interest in this because this is a mineral which is hyperactive it has a lot of values you know in present day science and technology and but it used to be a treated as a curse sometime back so you go to the central parts of India Maharashtra Madhya Pradesh Karnataka where you have black cotton soil the constituent of the black cotton soil is monodonite it has very strong affinity towards environmental changes during rains it will accumulate water in it becomes fat and when rains go it shrinks any building which is sitting on the blank black cotton soil deposits monodonitic soils is bound to get distressed crack conditions will fail and the reason is this is silica alumina silica combination and in between the platelets you will have water and this water is weakly attached because of Vendor ball forces so I hope you remember formula 10 plus 2 chemistry hydrogen bond is much stronger than Vendor ball force correct so this is how it goes so more strength and the more stability comes because of the weak bonds as compared to the chelonitic material so because of this system the water enters into these platelets the spacings and the water hunger for this mineral is extremely high alright it has a lot of value in agriculture but as far as cell engineering practice are concerned people want to bypass this because they do not want to keep any foundation on this type of systems but in sports it is becoming useful because this is what is known as smectite the smectite is one type of monodonite which is to be added to make pitches very stable for the required duration alright and then you as I was giving the logic captains they want to water the pitch after the first innings are over second innings are over and so on and they want to roll it with a light roller heavy rollers all the dynamics will come into the picture a little bit more on the monodonite because this is of special interest is a highly reactive expansive clay as I said last time it is not expensive it is expensive it expands and this is the formula for the monodonite n times water molecules indicates that n could be any number clear so it has a special hunger for water bentonite is one of the monodonite which we discussed earlier it is used in drilling slurry trench design leakages most of the putties which you use you know different types of putties which are used for sealing the cracks are made up of bentonite and this shows a thixotropic effect and if you remember this is the material which is normally used in nuclear industry for depositing of the disposal of the nuclear waste then comes the elite is another interesting mineral where the spacing between the alumina silica alumina sheets would be filled up with potash amines so normally potash amines go and sit over in between and again this is a very weak bond as compared to the hydrogen bonding or van der Waal forces so this is how the mineralogy is taken care of there is a mineral which is known as chloride so this is a 2 is to 1 is to 1 type of a clay mineral and we have workmeculite we have atapulite and all these are the minerals which are present in the in the in the soils depending upon your requirements you can work on them now let me talk about the clay particle because I wanted to start the discussion on on particulate nature of soils clay particles are platelets all right and when they are platelets they would have a fabric as I decide defined last time fabric is nothing but the texture now this is a subject which is in focus much more focus and attention of the researchers these days pharmaceutical guys and I hope you understand pharmacy is the profession where you know the money is too much both ways they deal with this type of structures a lot what is the interest can you can you imagine well these are the structures which have been created in which I can fill anything so these are the porous structures now what I am showing here are the platelets which is a depiction of a clay mineral or a clay sheet now clay sheets might sit like this that this is the sheet the face is touching the edge of another sheet and edges touching the face of another sheet this is what is known as edge to face contact when I will start discussing the mechanisms of movement of water in soils I will be referring to this as a flocculated structure if you compact this soil all right suppose if I confine it in a volume and if I compact it so all these platelets are going to get aligned very obedient all right so this is what happens you must have heard about the cart pack house structures all right so the moment you take a card structure you press it from both sides compact it a bit all the plate becomes aligned this is what is known as a dispersed structure face to face contact so face is in touch with another face porosity is less as compared to the initial status I will revisit all this this is something which is normally used as scanning electron microscopy for those of you who will be interested in such studies if you want to see the alignment of the particles of the fabric of the of the clay particles scanning electron microscope is the tool which is used to see what type of arrangement of the grains which I showed you is existing in the system I am not going to go into details of all these things these are slightly out of context for undergraduates but you should be aware of because this is where the R and D is and this is where the stakes are for our profession these are the images I mean just now I showed you some schematic diagram and here what you can see is the kaolin fabric look at this I mean sometimes you must have seen when you keep the loaves of the bread one over the other is it not this is how it looks like look at the sheets of kaolin these are the sheets of kaolin all right they are just tagged one over the other and there is a lot of porosity pores which are getting created in the system so this is a typical soil fabric so fabric word is used for two things one is orientation of the particles shape of the particles and the type of pores which are encased in them you understand so sometime back I was discussing about controlled drug delivery is it not what would I like to do I would like to inject drug into these cavities which are at nanometer level and they become medicines for me they go in the body and slowly they will release so gone are the days when people used to take pills and the you know capsules which used to react immediately and that reaction used to be fatal for the body nowadays you create a system through which the x-grass x-grass means something which comes out is slow controlled regulated fine so imagine you need not to eat food you just eat few capsules what your astronauts do in those minerals they must have packed nutrition so much that each capsule will slowly release in your stomach and it will go in the blood vessels and you can stay without eating anything for whole day is this correct another view of how the plate limit plate plates look like you know this is another fabric beautiful plates stacked with each other look at this edge to edge all right look at this plate let and this plate let edge to edge face to edge this is the face and this is the edge okay bundles or the sheets of minerals lying one over the other first story second is this is the first story second story on the top of this is there this is there complete stack is like this so face to face to face to face clear in between whatever space is there can be utilized by soil technologies just to give you a feel of this please remember the scale this is 200 nanometers all right so all these studies are some micron studies you have to have a lot of patience you have to have a lot of time to sit down take images quantify them many of you who are trying to work on artificial intelligence associated with agricultural projects there are a lot of projects going on in the country where by looking at the color by looking at the shape morphology people are trying to work out on what type of agricultural doses should be given to the vegetation a lot of projects are going on they use many a times SAR photogrammetry also SAR images remote sensing data they use so all these are you know can be utilized by the guys who are in the profession those of you might be interested in microbial studies because I talked about microbes I thought I will just show you how the microbes look like can you identify these microbes all these white white capsules which you are seeing over there these are the microbes 20 micron is this much so imagine the size of the microbial activity this would not be even one micron or something like that all right so nowadays people are talking about this a lot this is at 5000 magnification of the image scanning electron microscopy is a closer view I just wanted to see how the clay platelets are adhering the bacteria densely populated colonies of bacteria in the soils you know so what they are going to do what type of failure they are going to create this is a profession which is known as forensic geotechnical engineering why systems are failing though they were designed in the best possible manner clear so we can show what type of movement and where the concentrations are and the way you want to interpret it I mean you become a forensic expert why failure has occurred then comes the x-ray diffraction because you must have noticed that most of the minerals have a elemental composition and their oxides mostly SiO2L, Al2O3 and so on so the question is how are you going to find out the oxide composition of the soils so this is what is done with the help of x-ray diffractor meters we call them as x-ray diffraction analysis XRD analysis how many of you know Bragg's law what is the application of Bragg's law with respect to this so when you are studying 10 plus 2 phases you simply mugged it up no now the applications are coming so your 2d sin theta equal to n lambda agreed so what is n number of wavelength or whatever lambda is the wavelength and 2d sin theta what is the distance between 2 layers of particles stacks very good so atomic distance clear and sin theta theta is angle of incidence of the x-rays so you take the sample keep it on a platform and allow the x-ray to fall on this with some angle theta that you can measure and you know what type of wave you are using which type of filter you are using copper K alpha or you know nichrome chromium whatever that you know so you know the wavelength of the wave and it is hitting the sample and whatever the reflected wave is if I can capture it on a electron sensor or if this electron beam is captured on a analyzer I know the pattern so I will show you whatever patterns you get and then you can know quickly what are the elements which are present this is so whether you are from a gem sorry you know jewellery shop or you are a artist or whatever everybody uses XRD analysis you must have seen you go to jewellers what do they do they will put the gel there and then immediately tell you what is the component of the carbon how much is this gold silver and so on I will show you how to read these things quickly so if you want to know the molecular lattice and crystal structure of the minerals then you have to do XRD analysis now this is becoming more research oriented I hope you are realizing the concepts are same but I want to identify you remember minerals how to identify them all these are identification tools then quantification softwares are there nowadays you are lucky that you just feed the data and you know what is the composition of the soil in terms of the minerals and then I can give a sort of a prescription how to utilize this there is something known as the DTA differential thermal analysis so every mineral will have a specific heat and that is the keyword clear so whatever minerals you are using so suppose if you join tomorrow oil and gas industry where they are very much eager to design slurries which can be injected up to let us say 10 kilometer deep inside the seabed so that I can seal the well check it on net deep cementing slurries is a beautiful subject a lot of money is there there is a lot of companies who sponsor and who hire people for designing deep cementing slurries so what should be the component of these slurries how what type of liquid should be utilized what is their thermal property what is their pressure bearing and all these things you can study by doing these tests. So typical diffractograms you find all these type of diffractograms normally in in hospitals is it not or when you meet a surgeon what he does or she does so cardiogram cardiogram is a sort of a record of how your heart is functioning same thing we are doing here so D is the atomic spacing in Bragg's law that is what I am trying to find out so these typical graphs look like this on y axis you have relative intensity and the x axis you have 2 theta value of a ray clear what I have to do is expose the sample get this type of a diffractogram I can I will be knowing theta value and the peaks of the minerals which are present in the system fortunately all this is done nowadays with the help of software. So if you click over here ICSD you will go to a webpage which deals with the database of minerals there was a time when my students used to sit down and match the D value up to 4th decimal place they used to spend months together now things are very state of the art it is a matter of few minutes when you can get the results but yes how to use the results judiciously is a big question this is what is known as inorganic crystal structure database quick reflection of the graphs which you are going to get sometimes you get peaks crystalline material very inert sometimes you get hazy pictures without any clear peaks so that is the difference you know this type of material is a good classy phase material this can be utilized as a cement the more and more peaks you have the more and more crystallinity very stable system so as a geotechnical engineer I would like to utilize the soils which are crystalline in nature not amorphous this is the amorphous nature this is the crystalline nature clear but suppose if I change my profession and if I am doing let us say medicine pharmaceuticals I do not want crystalline thing these are going to scratch my intestine from inside is it not I cannot use it in the detergents I cannot use it on in washing soaps so what I have to do I have to use a amorphous phase of the material which is soft gentle very high cation exchange capacity very high surface area clear so this is the difference depending upon your profession you can select the right one okay so having done the minerals now let me touch upon the particulate nature of soils soils by virtue of their nature are particulate in nature until now you have done fluid mechanics alright and at the same time you have done solid mechanics also ever wonder that why should we study the mechanics of soils very interesting philosophy it is a wonderful material and it is a all rounder so most of the captains prefer all round rules no in their team given a chance this material can behave like solids and it also can behave like fluids did you understand this concept unfortunately the conventional geomechanics only deals with this state but most of the projects in civil engineering you will find are related with slurification of the soils making different types of you know emulsions different types of slurries I give you an example of last time dredging so those of you are going to be an expert in dredging would make a slurry of the soils which is going to be in the fluid state so I hope you can realize this interesting behavior of the soils a material you can use the way you want what is controlling these two transitions the moisture content you keep on increasing the moisture in the soils they get translated to a fluid state they start flowing and hence you have to study the fluidity of the soil so we will use a term which is known as flow index of soils when we characterize the soil alright because in a flowing state I told you the examples in modern day geotechnical engineering practices wherever you want to make a slurry mentonite make a slurry put it in the in the piling put it behind the retaining walls for stability and so on dredging solids now this is what actually we are going to concentrate more on if I start from the fluid state of the soils and if I keep on drying the soil it gets converted to the solid state and again the interplay of the moisture now what is meant by the particulate system is basically soil particles are not bonded so when we say particulate nature that means the soil is treated as a consortium of particles of different sizes different shapes different morphology or whatever so these soil particles are not bonded strongly as in case of the metal crystals so they are free to move freely the second analogy is that soil particles are solids and hence cannot move freely so this is a state of the solid system this is a state of the fluid system now little bit of the mechanics of the material because we are talking about the particulate nature of the soils so henceforth now the discussion is going too much mechanistic those of you who are having complaints that is all abstract theoretical now should gear up for learning the mechanics part of this I am sure you will find it equally critical if not I should not use the word difficult you must be hearing the names of finite element discrete element continuum and all these things some of you might be working also or might have worked during your internship with the different universities there are many guys who work in the continuum mechanics discrete mechanics so soils by nature are a consortium of discrete particles this is statement correct discrete particle means each particle has its own identity but the beauty is that all these particles put together form a continuum this is okay fine so suppose if I consider a control volume and for the sake of simplicity this contains soils the way I am showing it is a general soil rounded particles very discrete particles a granular system and this system is being compressed by applying a pressure and your J and all this you must have done hundreds of example problems like this but there is a difference now what is the difference the material is new this material you have not studied yet had it been fluid you could have done easily pressure diagram you know constant pressure and hydro static pressure and you will sum it up and you will say this is the pressure now the tricks start so if I am applying stress normally I define normal stress as sigma these are normal stress now the system is very moody it all depends upon the confinement you learn these words because unless you learn these words there is no fun clear so the subject makes you understand the terms and the terminologies which are being used in the most technical way now this is the confinement had it been a homogeneous system I use the word discrete system it is not homogeneous system like fluid not like gases imagine if the confinement is rigid you have done all this mechanics rigid body mechanics solid mechanics you have done your masters in that now suppose if I put a condition that this system is not rigid and this becomes flexible now what you will do that is what we are going to study you agree why it is flexible now what I have done is very conveniently to make you understand what we are discussing this is the ground level you remember and I have taken a small control section out of this in ground very rarely you will find that the boundaries are going to be rigid unless you place sheet piles agreed now these sheet piles are the elements of the steel which are you must be seeing all along the highways you know they what do they do they embed to sheet piles 10 sheets and then they can excavate in between they make basements underground space metro is being done right now go and see that so the chances are that you are not going to have the confinements which are rigid had this been rigid and if I asked you how the pressure is going to get delegated inside the system it was fairly simple you would have taken a element out of this and you would have zoomed it saying this is a particle this is a particle and when I am compressing them they come closer to each other and what is going to happen if the compressive forces are extremely high then the crushing strength of the grains is this okay if the confining stresses are higher then the crushing strength of the grains what is going to happen up to a certain limit they will come close to each other the pressure intensity will keep on increasing at this point and then the pressure will increase so much that this might be the situation you understand they will come closer to each other first because you are compressing them in a rigid system lateral deformation is 0 the only possibility is the whole system will move down get compressed particles will come closer to each other beyond the crushing strength of the particle the contact remains the stress keeps on building over here the stage comes where the crushing takes place this is the crushing of grains one mechanism in geomechanics you are designing the building foundations the stress intensity is so much which is much more beyond the crushing strength of quartz 20 MPa the particles will get crushed if I draw the free body diagram there is a normal stress acting over here there is a shear stress acting over here clear the normal stress is higher than the crushing strength and hence this is the first mechanism which controls the deformation of the soils is this part clear deformation of the soils now when we talk about deformation it is understood that we are talking about the granular system there is another possibility that I might be having some fine-grained particles also in this so these are the fine-grained materials clays, silts, fine sands now what is going to happen they provide a sort of a cushion so this type of situation will not occur I can idealize this situation as a clay platelet which is supported on two coarse-grained materials and I am sure you are doing this analysis a lot in structural analysis is not the loading comes and you know what is the deformation of this system if I keep on increasing the stresses the stage will come where the clay platelet itself will break so this is the second deformation mechanism for the soils we call it as a particle crushing this is what is known as particle bending and the third one is what is known as particle shearing or rolling in this case the chances of rolling are going to be absolutely zero why because I said this is a confined rigid system there is no lateral deformation the only possibility is the more and more stress you apply the load which you are applying is getting converted into the form of the stress and this stress might create a shear stress and because of the crushing incapability of the material the system crush crush the moment this confinement becomes flexible which is the situation in most of the cases now what is going to happen and if I take the particulate behavior of the soils and suppose there is a consortium of particles now imagine if I am loading it from the top the boundaries are flexible it is a semi-infinite soil mass both sides the soil mass exist infinite clear what is going to happen this particle will push it create some space this particle gets shifted in the little direction and in the process it might so happen that one of the particles might roll over and come and sit let me create few more particles to make my point clear okay the moment you compress it you apply loading on this the chances are this particle go and come and sit over here like this this may come out and this may come and sit over here like this this is what is known as rolling process this is what I was writing here so this is the C mechanism so deformation of the system which we were talking about which is the particulate in nature depending upon the boundary conditions would be either a b or c or a combination of the three it is okay so this would be either a b c or combination of a b and c depending upon the constituents of the material the fraction or the you know the type of mechanism which is going to supersede others would change these are the hypothesis henceforth the entire discussion would be only in this form so what I have done I have done two idealization first is the material granular material encased in a rigid box the boundaries are not going to deform when you make wells foundation wells for you know very important bridges like Brahma Putra valley there are so many bridges which are being done most of the wells are being done by this concept what I have to do I have to create a confinement deep inside the riverbed insert something so that the soil does not deflect move out of the control volume and lay the foundation on the top of this you are happy now the foundations are coming in picture so onshore when you are working the situation could not be like this and this system might be flexible and hence all this is going to happen so what we have done is material material approximation and the mechanism approximation